The invention relates to a device for detecting or following the position of a bone according to the preamble of claim 1. The invention further relates to a system which includes this device.
In medical operations, it is necessary in certain circumstances to obtain data on the internal structures of the body prior to the operation, for example by means of a CT scan or an MRI scan, and then to make this data available to the operating physician during the operation, for example on a monitor. The problem is that, during the operation, the internal structures of the body may be displaced, for instance, by the respiratory movements of the patient or by the surgical intervention of the physician. A displacement of a bone, however, means that the previously recorded images no longer represent the actual position of the bone and as a result during a surgical intervention the physician may plan the wrong approach.
Devices which measure a movement of a part of the body and determine and follow the instantaneous position of the part of the body are known. These devices work with position indicators in the form of, for example, radiation emitters which are fastened to supporting frames. The supporting frames in turn are secured to the part of the body. In practice, it has turned out that although the fastening of position transmitters to such frames permits position determination of the frame and thus also position determination of the part of the body held in the frame, the accuracy of such position determination is in need of improvement since the supporting frames are not fastened to the bone directly but, for example, to the head or to the arm. Moreover, slight displacements between the part of the body and the frame cannot be ruled out with certainty.
In order to avoid the problems associated with such frames, DE 295 03 001 proposes dispensing with the frame and instead of this fixing the position indicators directly to the bone with the aid of bone screws. The bone screws in this case have a screw body which acts as a holder for the position indicator.
However, the device for detecting or following the position of a bone known from DE 295 03 001 also has a series of disadvantages. For instance, both the fastening and the release of the bone screws are associated with expenditure in terms of time and apparatus. This problem is particularly pronounced when the screws have to be placed inside the patient""s body. Moreover, owing to the impairment of the bone caused by the screwing-in, it is not possible to use bone screws as a holder for the position indicators in a large number of applications. A use of the device known from DE 295 03 001 inside the patient""s body is also frequently excluded because the position indicators, in the form of light-emitting diodes, received by the bone screws are difficult to see or cannot be seen at all during the operation. For this reason, the device known form DE 295 03 001 is in practice only suitable for detecting and following the position of a cranial bone.
The object on which the invention is based is to provide a device for detecting or following the position of a bone which can be fastened to a bone, in particular inside the body, and detached therefrom again in a simple yet reliable manner. Furthermore, the device is to be capable of being designed so as to simplify the detection of the signal emitted by the position indicator especially when the device is fastened to a bone situated inside the body. A further object finally is to specify a system for detecting and/or following the position of a bone which includes the device according to the invention.
These objects are solved by a device according to claim 1 and a system according to claim 13. The subclaims relate to advantageous refinements and developments of the invention.
According to the invention, in the case of a device for detecting or following the position of a bone, which comprises a holder for a position indicator, there is provided a gripping mechanism which is designed to surround the bone on two opposite sides and on a third side, and which executes a constrained movement in the direction of the third side as a result of the bone being surrounded on the two opposite sides. By means of the gripping mechanism, an optimum support at three or more points and an optimum flow of force is thus achieved in that, upon surrounding the bone on the two opposite sides, assisting kinematics ensure that the device is pressed against the bone on the third side.
The gripping mechanism allows fastening and detachment of the holder without the bone being damaged. In contrast to bone screws for example, the device can be fastened to the bone without an additional tool. This reduces on the one hand the expenditure in terms of apparatus for fastening and detaching the holder and on the other hand also the expenditure in terms of time associated with the fastening and detaching. Since the fastening of the holder to the bone is generally associated with a surgical intervention, the operating time is thus also shortened.
The gripping mechanism is preferably designed in such a manner that it comprises a pivoting mechanism with, for example, two or more pivotable gripping elements which cooperate with one or more further gripping elements in such a manner that the bone is surrounded on three or more sides by the set of gripping elements as a whole. An actuating device can be provided for the pivotable gripping elements. This actuating device allows the pivotable gripping elements to move relative to the bone and to the at least one further gripping element. Advantageously, the actuating device additionally allows the pivotable gripping elements to be locked in a position surrounding the bone.
The cooperation between a pivotable gripping element and the actuating mechanism takes place particularly preferably in such a manner that an at least regionally wedge-shaped element acts on a pivotable gripping element or on a plurality of pivotable gripping elements simultaneously. In this way, by movement of the wedge element the pivotable gripping elements can be actuated. It is also conceivable to use the wedge element to lock the pivotable gripping elements with a preset clamping force in a position surrounding the bone in order thereby to connect the holder for the position indicator firmly to the bone. A simple and reliable connection between the bone and the device for detecting or following the bone is thus ensured.
In a preferred refinement of the gripping mechanism, each pivotable gripping element is designed as a lever arm which is part of a rotatably mounted lever. The actuating mechanism can then cooperate, for example by means of the wedge element, with this lever arm or with one or more further lever arms of the lever.
A further refinement of the device provides for the holder for the position indicator to have an elongate portion which spatially separates the gripping elements from an operating element of the actuating device for the gripping elements. For instance, it is conceivable to arrange the gripping elements in the region of one end of the elongate portion of the gripping elements and to provide the operating element for the actuating device in the region of the opposite end. Such a refinement of the holder for the position indocator allows the operating element to be arranged spatially remote from the bone. This is expedient especially in surgical interventions, since a sufficient length of the elongate portion means that the operating element can protrude from the patient""s body. For the same reason, it is advantageous to fasten the position indicator likewise in the region of the operating element, i.e. at the end of the holder opposite the gripping elements.